1. Field of the Invention
The present invention relates to etherification and/or oligomerization, particularly dimerization, of propylene in streams containing C.sub.3 and C.sub.4 alkenes using acid cation exchange resin catalyst in the presence of methanol.
2. Related Art
Refinery streams such as catalytic cracker offgas often contain large quantities of propylene in a mixture with various C.sub.4 's (n-butene, isobutene, n-butane and isobutane). There has been a great deal of research directed to recovering the C.sub.4 's e.g., by etherification, fractionation and oligomerization using acid cation exchange resins, however, the C.sub.3 's which include propylene have generally been treated as inerts in these processes, in the same manner as isobutane and n-butane.
The reaction of olefins, including propylene to produce long chain polymers, using certain organo-metallic catalysts is well known. The best known catalysts are homogeneous catalysts consisting of compounds of metals of groups II to VI of the Periodic Table of Elements in combination with other compounds of metals of groups I to III, such as the Ziegler catalysts, which are preferably specific combinations of titanium halide and trialkyl aluminum component with or without other metal promoters. Alkyl aluminum halides in combination alkyl titanium esters are another example of a homogeneous catalyst used for this reaction. Low molecular weight polymers, i.e., dimers and trimers have been produced by using extremely low concentrations of these catalysts.
Similarly, free radial carbonium and carbanions have also been used to promote alpha-olefin polymerization and acid cation exchange resins have been used extensively for oligomerization, for example, U.S. Pat. Nos. 4,100,220; 4,215,011; 4,242,530; 4,232,177; 4,375,576; 4,463,211 and UK Patent Specifications 973,555 and 2,086,415B.
Other acid catalyst for oligomerizations include sulfuric acid (U.S. Pat. Nos. 3,546,317 and 3,832,418) and perfluorosulfonic acid resin (U.S. Pat. No. 4,065,512), phosphoric acid (Ipatieff, V. N., "Catalytic Polymerization of Gaseous Olefins by Liquid Phosphoric Acid", Ing and Eng, Ch. 27, No. 9 [1935] p. 1067-1071). In the vapor phase Ipatieff observed that phosphoric acid polymerization of propylene was accelerated by the presence of butene-1 or by polymerizing butene-1 prior to propylene. The product comprises primarily C.sub.9 and higher polymers. It was also found that butene-2 and isobutene had the same effect.
The etherification of propylene is not widely discussed in the art, and in fact it is not easily obtained in significant yields with acid catalysts, particularly the cation exchange resins. However, methyl isopropyl ether (MIPE) can be expected to be a desirable octane improver.
In the present invention it has been found that the reactions of propylene, namely etherification and/or oligomerization can be improved and controlled by having specified amounts of isobutene and methanol present during the reaction.
It is an advantage of the present invention that a liquid phase reaction may be carried out to etherify and/or oligomerize propylene in improved conversion from low value mixed C.sub.3 -C.sub.4 streams. It is a further advantage that a method is provided for the etherification of propylene with methanol in this low value stream, since methyl isopropyl ether will act as a gasoline octane improver. It is a particular advantage that a mixed product of oligomers, principally dimers and codimers of propylene and isobutene and methyl ethers of propylene and isobutene which comprises a valuable gasoline or blending stock may be obtained. It is a special feature of the present invention the oligomers produced are principally dimers which have higher octane numbers for gasoline blending than higher oligomers. It is an additional advantage that the presence of methanol in the reaction in the proper amount exerts a leveling effect on the catalyst such that the exothermic reaction proceeds at moderate temperatures without hot spots or polymer fouling in the catalyst bed.